Dear Steve,
No argument with any of what you say, except that I think you have misread "my definition" of Leonardo as an artist. Nor was I talking exclusively about friends. Rather, in the nature of what I do (and especially in the nature of going every year to Arles) I meet more dedicated photographers than most.
The most successful artists rarely put their art above accommodation -- they can't, as they need somewhere to work -- and indeed, quite a few of the artists I know actually own the roofs over their heads. Some don't. But they are mostly happy enough with functional accommodation: they prefer spending their money on photography to spending it on new furniture, fancy decor, the usual trappings of material "success".
Many work McJobs to support their habit, and that was my point: above a certain level of commitment/obsession, art tends to be a drug of addiction, not something you choose. You try to keep it under control. You don't treat it as a hobby.
Most artists I know are not all that good at relationships, but again, some are. All generalizations are notoriously dangerous, including this one, but I stand by my assertion that few people realize just how much hard work a serious artist is likely to put in to his art. Or of course her.
Cheers,
R.